Most likely the crankset is loose.
But it can be a ton of things. As mentioned above it can be a front QR skewer ( a little grease on the skewer and proper tightening solves this)
If you have a spare set of wheels, swap out wheels and see if the noise goes away, to rule out wheels.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.